1. Field of the Invention
The invention relates to an apparatus for displacing shaft-mounting bearing stands, which are secured to carriages, in carriage guides, preferably for displacing the bearing stands of plate cylinders and inking rollers of a printing unit is carriage tracks of the inking unit supports of a multicolor rotary press, comprising screw drives, which are driven by electric motors, preferably by stepping motors.
2. Description of the Prior Art
Such as apparatus for displacing the bearing stands for a plate cylinder and an inking roller of a flexographic press is known, e.g., from German Patent Specification 29 41 521. In that known apparatus the bearing stands for the plate cylinder are guided in carriage tracks of the inking unit supports and are provided with separate screw drives, the carriages for the plate cylinders are provided with further carriage tracks for the carriages which carry the bearing stands for the inking rollers, and the latter carriages are provided with separate screw drivers. Whereas that known apparatus is inherently satisfactory in operation, it is rather expensive owing to the provision of the additional carriages, which are guided in carriage tracks and are provided with additional carriage tracks for carriages that are displaceable thereon.
French Patent Specification 669,672 discloses a printing press which comprises a plurality of printing units and in which each plate cylinder and each inking unit associated therewith are slidably mounted by guide bushings on a common track tube and are displaceable by means of a single screw, which is provided with a drive. Each inking unit consists of an endless inking belt, which is associated with the plate cylinder and revolves around guide rollers. To permit a disengagement of the plate cylinder from the impression cylinder and a disengagement of the inking belt from the plate cylinder, the threads of the screw have different leads and that screw section which serves to move the inking unit has a larger lead than the screw section which cooperates with the plate cylinder, As a result, a rotation of the screw will impart to the inking unit a larger displacement than to the bearings for the plate cylinder. But that known apparatus has the disadvantage that the plate cylinder and the inking unit cannot be moved independently of each other but both perform predetermined movements relative to each other as the screw is driven. For this reason it is not possible in the known apparatus to force the plate cylinder more strongly against the impression cylinder without a change of the contact pressure of the inking belt. It is also not possible to force the inking belt more strongly against the plate cylinder and at the same time to force the plate cylinder less strongly against the impression cylinder. Owing to the fixed coordination of the relative movements of the bearing stands for the plate cylinder and of the inking unit it is also not possible in the known apparatus to perform a so-called clean-up printing in that the inking belt is disengaged from the inking roller when the print operation has been proper completed so that the inking roller and the plate cylinder contacting the impression cylinder can then perform some additional revolutions, the remaining ink is thus removed from the inking roller and the plate cylinder and is applied to the material to printed, which passes through.